Effect of Ca2+ on the 1H NMR chemical shift of the methyl signal of oversulphated chondroitin sulphate, a contaminant in heparin

Abstract

The chemical shift of the methyl signal of oversulphated chondroitin sulphate (OSCS) is dependent on the type and concentration of the counterion. When OSCS is present as a contaminant in heparin sodium, the reported methyl 1H chemical shift is 2.15±0.02ppm. In this report, a value of 2.18±0.01ppm is reported for the OSCS in the presence of Ca2+. The chemical shift of the methyl signal of pure OSCS varies linearly from 2.13ppm to 2.18ppm with increasing amounts of Ca2+, until reaching the saturation point of four Ca2+ ions per OSCS disaccharide unit, which contains four sulphate groups (a 1:1 ratio between sulphate groups and Ca2+). This Ca2+ effect can be used for OSCS identification as well as to facilitate quantification.